The present invention relates to a tungsten sputtering target and its production method, and in particular relates to a sputtering target capable of forming thin films for semiconductor devices having low resistance and which are stable, as well as to the production method thereof.
Semiconductor devices are being demanded of further miniaturization and higher integration each year, and improvements in production processes and research for new materials are being actively conducted. For instance, as gate electrodes, polycrystalline silicon and metal silicide are generally used, but research of using a gate electrode made completely from metal (metal electrode) is being conducted for attaining even lower resistance. Consequently, by combining this kind of gate electrode and high dielectric constant gate insulation film, faster speed and lower power consumption are enabled.
With certain semiconductor devices, W (tungsten) is being used as the foregoing metal electrode. A tungsten film (gate electrode) is normally formed by sputtering a tungsten target. Patent Document 1 discloses a W target containing 0.01 to 1 wt % of Ni for forming a part of the gate pattern; that is, for forming tungsten silicide. Furthermore, Patent Document 2 discloses a W target containing 10 to 30 at % of Ni for use in forming a barrier film.
Nevertheless, the thin films formed from the foregoing targets encountered a problem in that the specific resistance could not be sufficiently lowered. In particular, when using a gate electrode, if the specific resistance can be sufficiently lowered, the film thickness of the gate electrode can be thinned by that much. However, with a conventional W target containing Ni or the like, the foregoing benefits could not be enjoyed. Furthermore, conventionally, no particular attention was given to the evenness (uniformity) of the specific resistance.